Transparent substrate coated with a stack of thin layers

This application is the U.S. National Stage of PCT/FR2022/050232, filed Feb. 9, 2022, which in turn claims priority to French patent application number 2101265 filed Feb. 10, 2021. The content of these applications are incorporated herein by reference in their entireties.

The invention relates to a transparent substrate coated with a stack of thin layers comprising a silver-based functional layer and also a glazed unit comprising such a substrate.

The invention also relates more particularly to the use of such substrates for manufacturing reinforced thermal insulation glazed units with a high solar factor. Such glazed units are for example intended for cold climates to equip buildings, in particular in order to reduce the heating effort in winter (so-called “low-emissivity” glazed units) and to maximize the free solar supply.

The solar factor SHGC is defined as the ratio between the solar energy gain entering the premises through the glazed unit and the incident solar energy. According to the NFRC 200-2017 standard, the solar energy gain is the sum of the energy flux transmitted directly through the glazed unit and the energy flux absorbed and then re-emitted toward the inside by the glazed unit.

A type of thin-layer stack known to confer such thermal insulation properties consists of a silver-based functional layer (or silver layer).

Silver-based functional layers are useful in several respects: by reflecting infrared, thermal or solar radiation, they impart on the material low-emissivity or solar control functions. Since they are electrically conducting, they also make it possible to obtain conducting materials, for example heating glazed units or electrodes.

Silver-based functional layers are deposited between coatings based on dielectric materials (hereafter known as dielectric coatings) which generally comprise several dielectric layers making it possible to adjust the optical properties of the stack and to preserve high transmission in the visible spectrum. Furthermore, these dielectric layers make it possible to protect the silver layers from chemical or mechanical attacks.

Application WO 2012/127162, belonging to the applicant, discloses a transparent substrate equipped with a stack of thin layers comprising a silver layer positioned between two particular non-metallic dielectric coatings making it possible to increase the solar factor of a glazed unit equipped with such a substrate and to obtain an acceptable coloring, in particular in transmission.

For this purpose, the stack preferably comprises:

Application WO 2017/42463 also belonging to the applicant, also targets coated transparent substrates making it possible to increase the solar factor of the glazed unit. The following stack is for example described in Example 1: Substrate/SiN/TiOx/SiZrN/ZnO/Ag/NiCr/ZnO/TiOx/SiO. The solar factor is however insufficient.

Document WO 2018/165357 (Guardian) is also known, which discloses an article coated with a low-emissivity stack, and in particular the following stack: Substrate/SiN/ZrSiN/TiO/ZnAlO/Ag/barrier TiO/ZrSiN/SiN/SiO. The ZrSiN layer must include more Zr than Si and therefore has an index close to that of the TiOlayer.

Application WO 2007/101964 discloses, in the case where the dielectric coating located below the silver layer comprises at least one dielectric layer based on nitride, in particular silicon and/or aluminum nitride, dielectric coatings comprising:

In this document, all the thin layers of the top dielectric coating, having a thickness of greater than 5 nm, have substantially equal refractive indices.

Consequently, the dielectric coatings consisting of such thin layers form a medium with a substantially homogeneous refractive index although the materials that constitute them are different.

There is strong demand for glazed unit combining the following properties:

The solar factor of the glazed unit “SF or g” is understood to mean the ratio in % of the total energy entering the premises through the glazed unit to the incident solar energy. The solar factor therefore measures the contribution of a glazed unit to the heating of the “room”. The smaller the solar factor, the smaller the solar inputs.

The heat loss coefficient also referred to as “Ug value” expresses the heat flux per meter of the glazed unit caused by a temperature difference existing between the outside environment and the inside separated by the glazed unit. The lower this value, the lower the heat losses and the better the insulation.

The performance of low-emissivity glazed units is based on the compromise between the solar factor that must be maximized (solar energy input) and the value Ug that it is necessary to get as low as possible (thermal transmittance indicating the heat losses of the glazed unit).

Achieving a low solar factor and low heat loss in tandem is difficult. To achieve low heat loss, in particular with stacks having a single silver-based functional layer, the emissivity of the multilayer must be reduced without increasing the absorption or the reflection.

However, it is very difficult to reduce the emissivity without reducing the light transmission. Indeed, increasing the thickness of the silver layers makes it possible to lower the emissivity and therefore to achieve a lower thermal transmittance Ug, but this occurs at the expense of light transmission. Insofar as the reduction in light transmission also causes a reduction in the solar factor, this solution does not make it possible to maximize solar inputs.

Thus, the development of glazed units with a low Ug value and a high solar factor is essential to improving the energy efficiency of buildings incorporating these glazed units.

The applicant has discovered, surprisingly, that when the dielectric coating under the functional layer is formed of layers that form a gradient of increasing index starting from the substrate and that the dielectric coating above the functional layer is formed of layers that form a gradient of decreasing index, it is possible to increase the solar factor while retaining a low emissivity. It is then also possible to reduce the thickness of the functional layer.

The invention relates to a transparent substrate coated with a stack of thin layers as defined in the set of claims. The thin-layer stack comprises, from the substrate, a bottom dielectric coating, a silver-based functional metal layer and a top dielectric coating, each dielectric coating including several dielectric layers. The bottom dielectric coating includes a series of at least three dielectric layers having increasing refractive indices, the index difference between the three layers being at least 0.15, a smoothing layer and a wetting layer, preferably based on zinc oxide (ZnO). The top dielectric coating comprises a zinc-oxide-based layer and a series of at least two layers having decreasing refractive indices.

The solution of the invention constituted by the choice of particular dielectric layer sequences makes it possible to optimize the optical filter and to increase the conductivity of the silver. These two improvements contribute to increasing the solar factor without impacting the heat loss coefficient Ug.

The transparent substrate coated according to the invention may have the following characteristics alone or in combination:

According to an advantageous embodiment, the top dielectric coating comprises at least the sequence of thin layers deposited in the following order above the functional layer

According to an advantageous embodiment, the top dielectric coating, located above the silver-based functional metal layer, comprises:

Preferably all the dielectric layers of the top dielectric coating, deposited above the zinc oxide layer, form a gradient of decreasing index.

In particular, each layer of the bottom dielectric coating having a thickness greater than 3 nm other than the wetting layer and the smoothing layer, forms a gradient of increasing index.

The stack is deposited by magnetic-field-assisted cathode sputtering (magnetron method). According to this advantageous embodiment, all the layers of the stack are deposited by magnetic-field-assisted cathode sputtering.

The invention also relates:

The preferred features which appear in the remainder of the description are applicable as well to the substrate according to the invention as, where appropriate, to the glazed unit, the method, the use, the building or the vehicle according to the invention.

All the described light features are obtained according to the principles and methods of the ISO 9050 standard relating to the determination of the light and solar features of the glazed units used in glass for the construction industry.

Conventionally, the refractive indices are measured at a wavelength of 550 nm.

According to the invention, two elements such as layers or substrates have substantially equal refractive indices when the absolute value of the difference between the refractive indices of the two materials constituting said layers or substrates at 550 nm is less than or equal to 0.15.

According to the invention, layers are considered to have different refractive indices when the absolute value of the difference between the refractive indices measured at 550 nm of the two materials constituting them is greater than or equal to 0.15, greater than or equal to 0.25, greater than 0.30, greater than 0.40, greater than 0.50, greater than 0.60, greater than 0.70 or greater than 0.80.

Unless specifically stipulated, the expressions “above” and “below” do not necessarily mean that two layers and/or coatings are positioned in contact with one another. When it is specified that a layer is deposited “in contact” with another layer or with a coating, this means that there cannot be one (or several) layer(s) inserted between these two layers (or layer and coating).

In the present description, unless otherwise indicated, the expression “based on”, used to characterize a material or a layer with respect to what it contains, means that the mass fraction of the constituent that it comprises is at least 50%, in particular at least 70%, preferably at least 90%.

Thus, the total optical thickness of the antireflective coating consists of the sum of all the optical thicknesses of the dielectric layers constituting this coating.

The stack is deposited by magnetic-field-assisted cathode sputtering (magnetron method). According to this advantageous embodiment, all the layers of the stack are deposited by magnetic-field-assisted cathode sputtering.

Unless otherwise mentioned, the thicknesses alluded to in the present document are physical thicknesses and the layers are thin layers. Thin layer is understood to mean a layer having a thickness of between 0.1 nm and 100 micrometers.

Throughout the description, the substrate according to the invention is regarded as laid horizontally. The stack of thin layers is deposited above the substrate. The meaning of the expressions “above” and “below” and “lower” and “upper” is to be considered with respect to this orientation. Unless specifically stipulated, the expressions “above” and “below” do not necessarily mean that two layers and/or coatings are positioned in contact with one another. When it is specified that a layer is deposited “in contact” with another layer or a coating, this means that there cannot be one or more layers inserted between these two layers.

The silver-based functional metal layer comprises at least 95.0%, preferably at least 96.5% and better still at least 98.0% by weight of silver, with respect to the weight of the functional layer. Preferably, the silver-based functional metal layer comprises less than 1.0% by weight of metals other than silver, relative to the weight of the silver-based functional metal layer.

In particular, the silver-based functional metal layer has a thickness between 5 and 20 nm, preferably between 6 and 10 nm and even more preferably between 7 and 8.5 nm. The silver-based functional metal layers have a thickness:

The stack may also further include a blocking layer deposited directly on the silver-based functional metal layer,

According to this embodiment, the blocking layer is chosen from metal layers, metal nitride layers, metal oxide layers and metal oxynitride layers based on one or more elements chosen from niobium Nb, tantalum Ta, titanium Ti, chromium Cr or nickel Ni or based on an alloy obtained from at least two of these metals. When these blocking layers are deposited in the metal, nitride, oxynitride, or sub-oxidized form, these layers can undergo a partial or complete oxidation according to their thickness and the nature of the layers which surround them, for example, during the deposition of the following layer or by oxidation in contact with the underlying layer.

The blocking layers are chosen from:

The blocking layers may in particular be, as deposited, Ti, TiN, TiOx, Nb, NbN, Ni, NiN, Cr, CrN, NiCr, NiCrOx, NiCrN, SnZnN layers.

Preferably, the blocking layers are based on titanium and are metallic layers or metal oxide layers, preferably, oxygen-substoichiometric.

According to an advantageous embodiment, the stack does not comprise a blocking layer located below and in contact with the silver-based functional metal layer.